Sweep circuit oscillator



Feb. 25, 1958 5, 55 1 2,824,962

SWEEP CIRCUIT OSCILLATOR Fil'd 001'. 25, 1955 2 Sheejzs-Sheet l '5 2 s m 0 |r|||- 0 T h 2 E :Q .2 g '2 o I S.

' s E *a 2 2 o a w m Q 09 O '5 a 2 INVENTOR. g '6 DAVID S. WISE ATTORNEYS United States atent i SWEEP CIRCUIT OSCILLATOR David S. Wise, Cleveland, Ohio, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application October 25, 1955, Serial No. 542,793

1 Claim. (Cl. 250-27) This invention relates to a sweep circuit oscillator and in particular to a linear sweep circuit oscillator for use with oscillographic equipment in which the oscillator can be calibrated to indicate writing speed and/or frequency of the oscillator.

In order to obtain a linear sweep, a linear sawtooth wave must be generated. The voltage across a capacitor is defined by:

where z '1 e-- 0 tdt e=voltage across a capacitor in volts.

C=capacity of the capacitor in farads.

i=instantaneous value of current flowing in the capacitor in amperes.

t=time in seconds.

T=total time in seconds the current i flowed into capacitor C.

If i=constant=l, then Equation 2 can then be rewritten as follows:

(4) E(v.olts)C'(;tf.) where E is the maximum potential to which the capacitor is permitted to be charged.

From Equation 4' it is apparent that if E is a constant, the frequency f isdetermined by the magnitudes of the capacitor C and'the current I. If several capacitors, the capacitances of'which are accurately known, are adapted to be connected to the sources of the constant current through a rangeorselector switch, and if the magnitude of the charging current'is accurately measured by a D. C. microammeter, then the value of the f can be determined. To do this, the ammeter is calibrated to give the vernier frequency of the sawtooth and the selector switch is calibrated to provide the proper decade multiplier.

-It is, therefore, an object of the invention to provide an improved linear sweep circuit oscillator, the frequency of which is accurately determinable.

ice

It is another object of the invention to provide a linear sweep circuit oscillator which has provision for driven and recurrent sweep.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein:

Fig. 1 is a block diagram of the sweep circuit oscillator; and

Fig. 2 is a schematic diagram of the sweep circuit oscillator. I

Referring now to Fig. 1, capacitor 10 is connected through D. C. microammeter 12 to a constant current generator 14. The voltage across capacitor 10 will thus increase linearly as a function of time and negatively. The potential across capacitor 10 is decoupled from bistable multivibrator 16 and output terminal 18 by a conventional cathode follower circuit 20. The characteristics of cathode follower 20 and multivibrator 16 are chosen so that when the voltage across capacitor 10 reaches a first predetermined magnitude the multivibrator will change from its initial state. Discharge circuit 22 becomes conductive to discharge capacitor 10 when multivibrator 16 changes from its initial state. Capacitor 10 then loses its charge very rapidly through discharge circuit 22. When the voltage across capacitor 10 has decreased to a second predetermined magnitude which is less than the first, multivibrator 10 returns to its initial state and causes discharge circuit 22 to become non conductive. The voltage acrosscapacitor 10 then builds up until it reaches the first predetermined magnitude again and thus the oscillator repeats the cycle.

In Fig. 2 the details of one form of the oscillator are illustrated. The major component of constant generator 14 is electron tube 24. In the generator illustrated, the magnitude of the current through tube 24 is controlled by the grid bias of tube 24 and the magnitude of the grid bias is varied by movement of the arm of potentiometer 26. Since direct current flows through tube 24 at all times, D. C. microammeter 12, which is connected in the plate circuit of tube 24, is used to measure the'magnitude of the current, and is calibrated to provide the Vernier reading of the frequency of the oscillator.

The output of generator 14 is connected through ammeter 12 and selector switch 28 to one of the capacitors 10a, 10b, 10c, 10d, 10c, or to external capacitor terminal 3%. By the use of large external capacitors, the magnitudes of which are accurately known, and which are connected between terminal 30 and ground, it is possible to provide lower sweep frequencies than it is convenient to provide by the internal circuitry of the oscillator.

In Fig. 2 terminal 18 and multivibrator 16 are isolated from the voltage across capacitor 10a by cathode follower circuit 20in which tube 31 is a major component. .The output from cathode follower 20 at ground level which permits D. C. coupling to the horizontal amplifier of an oscilloscope for good frequency responsecharacteristics.

Multivibrator 16 is a voltage sensitive bistable multi; vibrator. When the voltage across the capacitor 10a, for example, starts to increase, multivibrator l 6 will be in its initial condition with tube 32 conducting and tube 34 cut-off. When the voltage across the capacitor 14):: reaches a first predetermined magnitude, mult ivibrator 16 changes from its initial state to its second state in which tube 32 is cut-off and tube 34 is conducting. Multivibrator 16 remains in the second state until the voltage across the capacitor 16a decreases to the second predetermined magnitude, at which time multivibrator 16 returns to its initial state, i. e., with tube 32 conducting and tube 34 cut-ofi. The voltages at which multivibrator 16 changes states are adjusted by the use of variable load resistor 36 in the plate {circuit of tube 32 and the variable resistor 38 in the grid circuit of tube 34. Multivibrator '16 is frequency com pensated by the use of trimmer condenser 40 between the V plate of the tube 32 and the g'ridto'f tube 34'.

Tube42tof discharge circuit '22 is normally biased to cut-off so that current from generator 14 can only flow to capacitor a. 'When the voltage across capacitor 10a reaches the first predetermined magnitude, multivibrator 16 changes state. A positive pulse is applied from the plate of tube 32150 the 'grid of tube 42 and a negative pulse a is applied from the plate of tube 34 fo the cathode 'of tube V 42. The negative pulse is not essential for the operation 7 of the oscillator and'isfmerely injected asa form of-high frequency compensation. As a result, tube 42 conducts heavily to discharge capacitor 10a substantially instantaneously. When the voltage across capacitor lila reaches the secondpredetermined magnitude, multivibrator '16 again changes its state, and a negative pulse'is applied to- V the grid of the tube 42 and a positive pulse is applied to thecathode of tube 42 cutting; it off. Capacitor 10a is;

then free to store then-currentfrom source and start another cycle.

By changing the tinue to conduct when multivibrator 16' returns to its initial condition, i. e. with tube 32 conducting and tube 34 cut-on. Tube 42 will then draw enough current to pre- 7 value of the grid'rsis'toi' 44 the grid bias of tube 42 can be reduced so that tube 42 will con:

The values of the componentsr ofgenerator 14 were chosen, in this example of the invention, so that the magnitude of the current from generator 14could be varied, from 50 tarnpsnto 500- tamps.

ehesen as iet' or gronnd'pot'e tiaL; V r With thesevalues th'e'fr'equency rangewith capacitor with me from 1000.1 s tel-re, withj10d, from i vent anywoltage from-being builtrup on the capacitor 10a. The oscillator willfr'eniainin this condition Vuntil' negative and positive pulses of proper magnitudes are applied respectively to the negative gateoterminal 46 and a, the, positive gate terminal 48, or until a driving pulse" is appliedrto' terminal 52.

modified to provide a very stable driven sweep.

Thus the oscillator-can be 'Ifit is desiredto s'ynchronize th e o's'cillato'rjwith another signal, this signal can be applied-tothecathodeof tubes 32, :34 through potentiometer 50 an'dterminal'il 'In one embodiment of the invention the valuesof the components were as follows:

' sistance means in the gridcircuit of'the ,other multivitolOko, and with 108', from rote lO0'kc.1 i

The above values are exemplary of the'inventioriand V i are not to be construed as b eing'limitativet Obviously many modifications and .variatlonsr of the present invention are possible in theili'ght of the above-- teachings. It isftherefore to be-understood that'within t the scope of the appendfdelaimitheinvention niay'lie practiced otherwise than as specifieally -described.f

- Whatisclaimedisz V A sweep circuit oscillator comprisin gtia:cliargingfca f 4 pajcitor, a current generator circuit including a pento'de:

connected to'the charging capaciforfa bistable multivibrator havingpa first tube and a second tube providing an;

* initial state and a second state,ia cathode follower con- 1 V 7 meeting the output of .thecapacitor to saiditubes'of the j multivibrator' and being operable to change the muIti- A vibrator from its initial state to'its second state when V the voltage'across the capacitor-increases to a .first pre-.

determined valuega discharge circuit responsive torthe multivibrator output and operable to discharge theca 1 'pacit'or when the capacitor reaches, a secondxpredeter w mined value, said multivibrator returning from-its second c state to its initial 'state when the capacitor is discharged,

L a first variable resistance means i'n'theplate circuit of 7 one ofthe multivibrator tubes for selectively: settingthe initial state of the multivibrator and a' second variable rek brator tube for selectively settin'gthe second state of the Resistors;

R2 K '15K 15 K R 47K Rs 47K V R 15K 7 R 10K :R!) 15K Rm" 8 Ru 6.8K 2-R' 120K RR 1 K t Potentiometers: g a t 26 QK 7 o 7 i W 7 :44 v K. I f 50; f I, Tubes: 7 r V g '24 6AU6 WA -34. a 0 l V /2 12AT7' WA 12AT7 WA 7 multivibrator and a' potentiometer in the current gener i ator circuit for selectivelysetting'the grid bias of the, pentode to thereby establish a constautcharge rate" to the capacitor, 7 p K 7 References Cited inthe patent UNITED STATES PATENTS 2,265,29Q Knick V I p N r r 2,414,486 Rick e Jan. 2l', 1947 2,448,069 7 Ames'et a1 -Aug..3 '1,'1 948 2,448,070 Sustein Aug.-31, 1 948 2,562,188 3 Hance J ulyjl, 1951 2,576,339 Grayt. Nov. 27, 1951 The value of thefirst,predeterminedlmagnitude Was'choseii as '50 volts} and the value ofthe second predetermined magnitude was 

